The present invention relates to recording information about errors occurring while writing to a rewritable media.
Data is written onto rewritable media for storage and subsequent retrieval. Typically, the data is contained in one or more blocks. If an error occurs during a block write operation, another attempt is made using an error recovery procedure. Repeated attempts may be made using different error recovery procedures until a write is successful or the media is determined to be bad.
An exemplary rewritable media is magnetic tape. A typical magnetic tape access system includes a tape head with a write module and a read module trailing the write module in the direction of tape travel. The write module contains a plurality of write elements for simultaneously writing many data tracks. Similarly, the trailing read module contains a plurality of read elements for simultaneously reading the data tracks. Following each write element with a read element permits immediate read after write to verify that the data has been correctly written onto the tape. Write circuitry converts data into write module write signals. Read circuitry converts read module read signals into data. A drive controller controls one or more motors for moving the tape past the tape head in a particular direction and at a particular speed. A head position servo positions the head across the width of the tape to permit write and real elements access to appropriate data tracks. Head position relative to the tape is determined by reading servo tracks on the tape with servo read elements on the head.
If, during a write operation, data read by the trailing read head does not match the data just written by the write head, a write error has occurred. Write errors result from many causes including incorrect positioning of the tape head relative to the tape, incorrect tape velocity, debris on the tape, tape defects, and the like. Typically, when a write error is detected, the tape is rewound and one or more attempts to rewrite the data are performed. The tape system may sequence through a fixed set of error recovery procedures, each procedure including a rewrite attempt. If all rewrite procedures in the set fail, the tape is generally considered defective. At this point, an attempt may be made to recover any data that may be on the tape. The tape may then be analyzed to determine what problem caused the tape failure and to determine whether the problem was in the tape, the tape system, or both.
One difficulty encountered in analyzing a defective tape is in determining what types of problems were encountered with the tape prior to failure. Another difficulty is in establishing the error recovery procedure to minimize rewrite attempts. What is needed is to record the rewritable media write history for later analysis, particularly after media failure. The analysis should be usable for establishing error recovery procedure determination.
It is an object of the present invention to record write error recovery procedure history.
It is another object of the present invention to record information regarding the type of error causing a rewrite.
It is still another object of the present invention to optimize determining an error recovery procedure using an acquired history of rewrite attempts.
It is yet another object of the present invention to record the number and types of rewrite attempts without significantly modifying the rewritable media or the rewritable media access system.
In carrying out the above objects and other objects and features of the present invention, a system for recording the history associated with writing data onto rewritable media is provided. The system includes an access head for writing data onto the media and reading data from the media. A drive motor moves the media past the access head. A write formatter formats data into a device block to be written onto the media. A read formatter detects errors in data read from the media. A control unit determines an error recovery procedure based on an error detected in reading the media and enables the write formatter to insert an indication of the error recovery procedure into the device block. The error recovery procedure is then attempted. The process is repeated until either a successful write occurs or the media is determined to be bad.
In an embodiment of the present invention, the control unit determines an error type which is inserted into the device block by the write formatter. In a refinement, the write formatter inserts indications of the first error type and the most recently found error type into the device block.
In another embodiment of the present invention, the indication of the determined error recovery procedure is inserted into either or both of a header preceding the data and a trailer following the data.
In still another embodiment of the present invention, the error recovery procedure is determined based on a number of attempts to write the device block.
In yet another embodiment of the present invention, the error recovery procedure is determined based on a type of error detected.
A method of recording the history associated with writing data onto rewritable media is also provided. A device block comprising the data is formed. At least a portion of the device block is written. A portion of the device block is read. If an error occurs in writing the device block, an error recovery procedure is determined. An indication of the determined error recovery procedure is inserted into the device block and the process repeated.
Rewritable media having device blocks in at least one data track is also provided. Each device block includes an indication of the number of attempts required to write the device block.
A method of determining the history associated with rewritable media write errors is also provided. After writing a plurality of device blocks including an indication of the error recovery procedure used to write the block, each device block is read to extract the inserted error recovery procedure indication. Error recovery procedure determination may be modified based on the extracted error recovery procedure indications.
The above objects and other objects, features, and advantages of the present invention are readily apparent from the following detailed description of the best mode for carrying out the invention when taken in connection with the accompanying drawings.